Setting lasers: is there a "formula" for distance?

B

Biff Tannen

New member
Advice needed:
When setting a laser (such as the Crimson Trace) on a handgun, since the beam is not coming directly out of the barrel and therefore not 100% accurate at all distances simultaneously, it is preferable to set the laser to be most accurate for the approximate distance at which a person intends to use it.
And so, if a person adjusts their laser to be accurate at a close distance, it will tend to be less accurate at a far distance (and vice versa)...
But, I'm trying to find that "happy medium", if possible (without going through a bunch of ammo and range time to find out for myself)...
Is there a mathematical formula (or general "rule of thumb") which will help be predict how accurate the laser will be at other distances in relation to the one it is specifically set to?
Thanks!!
 
I only have a couple guns that are laser equipped, but here's what I do.

On the gun where the POI = POA (Sig P238 with CT Laserguard), I just put the laser dot to the sights at about 5-7 yards... that's plenty close enough for defensive work.

On the gun where POI is a bit lower than POA (S&W .38spl Bodyguard), I put the laser dot on the POI at 7 yards.

My "doctrine" for laser use is that the laser is NOT for precision. It is for super fast target acquisition in a defensive encounter. If it's an inch or so off, NBD- if I ever have to use it in defense, I'm putting the dot on center mass and going for it. It's for those times when I may not have time to use the sights. If I do have time to go for a more aimed shot, my intention is to use the sights and ignore the laser.
 
i basically use the same method as techno....i just want to be able to use the laser in an up close confrontation, especially in low light. If my bullets are hitting any where within an inch or 2 at 7 yards im good to go.
 
You have the same problem as with iron sites.


Lasers can actually be worse than irons, being below the bore there is only ONE point of intersection in many cases (irons usually have two).

The line of site is not the bore, ad so there is an error that varies with distance.

it is not a target shooting device.

Set it to put the holes 'close enough' over your expected rage.
 
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7 yards for my S&W 638. Not for target practice but great for low light sighting, and for point and shoot practice. Just point the gun without aiming hit the laser and see if you are on target. Best done with a unloaded gun. ;)
 
I sight mine at the longest distance of my hallway ~ 20 yards. There isnt much practical difference between 10-20 yards, and I don't see a need to sight it in under 10 yards, I can pointshoot well enough at that distance not to look for a red dot.
 
I sight mine for the longest distance I'm likely to shoot them. In the case of a J-frame, that would be 25 yards. (Not to say I'll never shoot one farther than that; KraigWY shoots his out to 100 yards...)

My rationale is that, at close ranges, the bullet will impact within 1.5" or so of the dot, and will get closer to the dot as the range increases to 25 yards.

OTOH, if I set parallax to close at 5 yards, then at 10 yards I have 1.5" the other way; at 15 yards, I have 3" the other way; at 25 yards, I have 5" of parallax induced.

I'd rather keep it at 1.5" or less within moderate handgun range.
 
MLeake:
I am fascinated by your answer, and hate to ask you this, but could you "dumb it down" for me? I just got my first laser and am trying to follow what you mean haha.
 
Ok, but I can't guarantee I won't go at least somewhat into the weeds. I'll try not to.

With the CTC grips on my old 442 (which is now my parents' 442; they needed a gun to go with their new carry permits), the laser sits approximately an inch down and an inch right of the bore. I don't have access to the gun, so I can't get more exact - this is an estimate.

Using right triangle geometry, the diagonal distance from the bore to the laser would be about 1.4"; the bullet would theoretically hit 1.4" away from the dot, 1" high and 1" left, to infinity. Of course, the bullet actually follows an arc, but the drop between zero and 25 yards is not much.

So, if I have the laser sighted parallel to the bore, without adjusting it at all, the bullet should stay 1" high and 1" left minus however far it drops over distance.

If I adjust the laser to the bore, I am actually aiming the laser at an angle high and left to the parallel line to the bore. The farther away I adjust the laser to intersect the bore line, the shallower that angle will be.

If I adjust the laser to intersect the bore line in close, say at 5 yards, I have induced an angle that will trend the laser 1.4" diagonally up and left every 5 yards. (It had to move up and over 1.4", 1" high and 1" left, to get to the bore line, and I made it do that in 5 yards.)

All intercepting angles will deviate to the opposite side at distances past the distance where they intersect the boreline. The steeper the intersecting angle, the more rapid the deviation at farther distances.

Hope that was somewhat more comprehensible.
 
MLeake wrote:
With the CTC grips on my old 442, Using right triangle geometry, the diagonal distance from the bore to the laser would be about 1.4"; the bullet would theoretically hit 1.4" away from the dot, 1" high and 1" left, to infinity.... So, if I have the laser sighted parallel to the bore, without adjusting it at all, the bullet should stay 1" high and 1" left minus however far it drops over distance... If I adjust the laser to the bore, I am actually aiming the laser at an angle high and left to the parallel line to the bore. The farther away I adjust the laser to intersect the bore line, the shallower that angle will be...If I adjust the laser to intersect the bore line in close, say at 5 yards, I have induced an angle that will trend the laser 1.4" diagonally up and left every 5 yards. (It had to move up and over 1.4", 1" high and 1" left, to get to the bore line, and I made it do that in 5 yards.)..All intercepting angles will deviate to the opposite side at distances past the distance where they intersect the boreline. The steeper the intersecting angle, the more rapid the deviation at farther distances.
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Thank you much, you really shed some light on that one!
So, if I am going for dead accuracy at any distance, I'm most likely best off having the laser point dead straight, and when aiming, pointing the lazer that theoreticly approximate 1.4 or so to the lower right of my target?
And, if I adjust the laser to the bore that theoreticly approximate 1.4 inches to the lower right of the bore at the distance of 5 yards, I have to anticipate to adjust my aim at 10 yards to point 2.8 inches to the lower right of my target?
And does this aim adjustment for distance adjust logarithmicly (doubling every 5 feet, 10 feet, 20 feet etc.) or does it just double every 5 feet?
Please forgive me in advance for all the questions, but a geometry wizzard I am not.
THANKS!!!
 
No problem.

Yes, if you are good at Kentucky Windage, you'll get the most accurate picture by sighting for infinity (IE parallel), and adjusting.

Most people prefer to sight in to some intermediate distance. I tend to sight in at the back wall of my LGS range (or did, when I had a laser).

If you adjust to an intersecting point, the rate of change will be linear, not logarithmic.
 
And, if I adjust the laser to the bore that theoreticly approximate 1.4 inches to the lower right of the bore at the distance of 5 yards, I have to anticipate to adjust my aim at 10 yards to point 2.8 inches to the lower right of my target?
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I have a CTC on a Commander and I have not found this to be true, if you have the laser adjusted roughly parallel to the bore.

As MLeake explained, you have converging lines up to POA/POI agreement and then diverging lines past that if you adjust the laser so it is not parallel to the bore but is "toed in" toward the bore.

While I can't believe it would be useful, you could also set up the laser for a diverging alignment (which is what you described) where the error would get worse the further from the muzzle. No POA/POI agreement, ever. This would be a "toed out" alignment.

What I did was to get as close as I could to parallel. I set up for roughly the same windage/elevation offset at 5 yds as the actual offset of the laser from the bore. That is, a group consistently an inch high and to the left of POA.

As the laser isn't any better at compensating for bullet drop than iron sights, you would need to "hold high" for some kind of distance shooting with the laser. But, as already noted, this is very unlikely. So, discount it.

If you set it up for "parallel", you will be within 1 to 2 inches of POA, from muzzle to 5 or 10 yds. Close enough in practice.

I have no idea why some instructions dwell on making POI=POA, other than a perceived marketing need. Maybe people feel some compulsion to set this up, like iron sights, and just aren't "happy" until they've achieved it.

If you think about converging/diverging lines, I'm sure you'll agree parallel is better, even though POI never equals POA.
 
MLeake & dmazur:
Thank you both very much, I found the "magic formula" I sought!
You have really opened up my eyes and affected my point of view immensely!
Thanks again and God bless!
 
If you have a rail to mount it to, then that simplified the double off axis situation.

You still have the issue that it is significantly lower htn the bore and you can set it pareal, and have it 1.X inches low for any reasonable distance you can shoot (or hit!)

I have two. One for range and one for HD. My HD I set for spot on at 10 yards (longest hallway). Good for any closer without adjustment and good for 20 yards the same (probably further but I am expecting anything further out is not a threat and or I can adjust as needed).

Prime use for me is night. Night sights or not, its very difficult to see iron sights, let alone fast aquasition.

So, while a laser is really not precision, by its use it does (or can) become precision as you know exactly where you are aimed and that's where your bullet will hit. You can shoot, or adjust and shoot if you are not where you want to be.

In an odd way it does become precision, as a good shoot is all about shot placement. It allows you to put the shot where it does the most good very quickly (in low light situations)

Like all things, I think its a tool and not perfect for all situations. You also need to come up with a tactical concept of its use. Any gun or weapon without a tactical doctrine is likely to fail you.

I do not just turn it on. Its off till I think I need it. So, I have a plan, know when and how I am going to use it. I also understand its capabilities and drawbacks and plan on those as well.

You may run into a situation that was not planned, but if you have thought out out it works, it will click and you can use it.
 
All of my pistol lasers are mounted under the front of the frame, about 1" below the barrel. I zero the weapon so that the bullets hit 1" high at 7 yds. That should keep the bullet within an inch of the laser's dot out as far as the dot will be visible. :cool:
 
All of my pistol lasers are mounted under the front of the frame, about 1" below the barrel. I zero the weapon so that the bullets hit 1" high at 7 yds. That should keep the bullet within an inch of the laser's dot out as far as the dot will be visible.
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Thank you for that logical, concise, cogent post. Sometimes I think some of us really do a lot of "overthinking" simple subjects. :cool: One of my pet peeves on forums like this is when guys use 1000 words to say what could be said in fifty-or-so. ;)

I just ordered a Crimson Trace CMR-201 universal rail-mount laser from Amazon. Should arrive next week. I'm going to try it first on one of my ARs, one that has a quad-rail gas block, and I'm going to mount the laser on the top. I currently have a red dot sight mounted on that particular AR, signted in @ 50 yds. I'll probably sight conform the laser to the red dot, if I can see the laser @ 50 yds.

I'll also try the laser on one of my 3rd gen Glocks. Will probably sight it in @ about 15 yds, to conform with the iron sights, more-or-less.

I have generally been of the opinion that lasers are pretty much only valuable as a tool for which to aggravate cats and dogs, but I'm going to give this one a try. If I don't like it, I can always send it back to Amazon! :p
 
eldorendo,

I'll take your peeve as being directed at me.

Since most CTC lasers are the grip type, and have dual axis offset, I assumed that was the type the OP was asking about. Based on that assumption, my answer had to be a bit more involved than Gary's was about the rail mount.

I agree that Gary's answer was nice and concise, but I would suggest he was also able to be so concise because a couple of us had already addressed the geometry and ballistics factors.
 
My bore sight laser is green. What I do is get about 21 feet from where I want the bullet to impact and turn on the green laser. I then look for the red dot of the CT and adjust the red dot until it is coincident with the green dot.

It works amazingly well.

Geetarman:D
 
Sometimes I think some of us really do a lot of "overthinking" simple subjects.
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I would rather have more explanation than less. Sometimes the subject is really not so simple and explanation is needed to make things understandable.

My work life was spent in dimensional metrology and I was always fascinated not only in what happened, but why it happened.

It carries over in my responses today.

Kraigwy is a prime example of one who can deliver the short answer and one who can delve into the details.

Geetarman:D
 
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